There are a few reasons this can happen but most open is if the system was powered off incorrectly. To fix this you will need to solidify the system again. I'm guessing you will find that the solidifier is currently disabled which is the default behavior with a corrupt inventory.
Solidcore scans the files on the disk and create an entry for each supported file in the scinv. Scinv file is updated when any changes with supported files are done in Update mode or via Updater. To track the integrity of scinv file, solidifier calculates the checksum of the scinv while every update and store it in the header of scinv. Solidcore calculates the checksum and matches it with the one stored in the header and if the two do not match, scinv (inventory) is considered as corrupt and machine is rebooted with solidcore disabled.
This can happen if the checksum did not get updated after scinv is updated/modified, most likely due to power failure or hard reboot.
Solidifier can be enabled again after machine is resolidified.